TELKOMNIKA
, Vol.10, No.2, June 2012, pp. 371~378 ISSN: 1693-6930
accredited by DGHE DIKTI, Decree No: 51DiktiKep2010 371
Received December 16, 2011; Revised April 24, 2012; Accepted April 27, 2012
Crosstalk Improvement of Polymer in Glass Thermo- Optical Multimode Interference Switch
N. Samdin, M. Yaacob, M.H. Ibrahim, A.B. Mohammad, N.M. Kassim
Lightwave Communication Research Group, Infocomm Research Alliance, Universiti Teknologi Malaysia 81310 Skudai, Johor, MALAYSIA
e-mail: haniffke.utm.my
Abstrak
Sebuah desain struktural baru yang menggabungkan atenuator optik variabel VOA dan saklar optik diusulkan dalam makalah ini. Desain didasarkan pada arsitektur interferensi multimode MMI dan
desiain ini telah menunjukkan peningkatan crosstalk saklar optik. Perangkat beroperasi dengan memanipulasi efek optik-termo TO yang secara alami ada di semua materi pemandu-gelombang optik.
Dengan menerapkan suatu polimer pada platform material kaca, VOA dioptimalkan dengan pelemahan optik 21,52 dB telah dicapai dengan daya 36,4 mW. Hasil simulasi menunjukkan bahwa VOA membantu
untuk mencapai perbaikan yang signifikan kinerja saklar optik khususnya di pengurangan crosstalk hingga 89,66.
Keywords : atenuator optik variabel, crosstalk, interferensi multimode, optik-termo, saklar optik
Abstract
A new structural design of combined variable optical attenuator VOA and optical switch has been proposed in this paper. The design is based on the multimode interference MMI architecture and it
has been demonstrated for crosstalk improvement of optical switch. The device operates by manipulating thermo-optic TO effect that naturally existed in all optical waveguide material. By applying a polymer on
glass material platform, the optimized VOA with optical attenuation of 21.52 dB has been achieved with applied power of 36.4 mW. The simulation result shows that the VOA helps to achieve significant
improvements of optical switch performance particularly in crosstalk reduction up to 89.66.
Keywords : crosstalk, multimode interference, optical switch, thermo-optic, variable optical attenuator
1. Introduction
High speed and high capacity optical components are crucially needed in current optical networks. For this, it is very necessary to research for good and tolerable performances of
optical switch. Furthermore, it is important to develop optical devices with low power consumption and crosstalk. Interestingly, multimode interference MMI structure is a good
candidate for these purposes. Although numbers of MMI optical switches have been developed which progressively claimed low switching power results, the crosstalk issue is yet to be solved.
Variable optical attenuator VOA is a device that functions to adjust optical power in the optical devices interconnection system. Few types of VOA structure have been developed; for
example Mach-Zehnder interferometer MZI based VOA [1-3], straight waveguide based VOA [4-6] and multimode interference MMI based VOA [7-8]. From the survey on type of developed
VOA, it shows that the MMI structure have the smallest power consumption; 7.8mW [8] compared with other type of VOA structure. Obviously, the MMI structure is a good candidate
for VOA design. For MMI-VOA structure, there two types of VOA that have been develop previously
which are; a combination of two MMI structure to be operate as MZI-VOA [9] and single MMI- VOA [10]. In the MZI-VOA, the structure is composed of an MMI power splitter with single inputs
and re-combined with double output to the other MMI combiner with single output. The active region induced by electro or thermo effect is located at the phase shift arms and used to
change the relative phases among the arms, which can realize the attenuation function [11]. Concurrently, a single coupler of MMI-VOA is realized through refractive index modulation. The
refractive index modulation leads to the variation of the imaging intensity within the MMI region. As a result, the output images can be attenuated which further realize the attenuation function.
ISSN: 1693-6930
TELKOMNIKA
Vol. 10, No. 2, June 2012 : 371 – 378 372
Notably, thermo-optic effect is the most popular approach to attain refractive index modulation in heated dielectric material. Thermo-optic coefficient, dndT is an important optical
constant related to thermo-optic effect. Typically, for polymer dndT ~ -10
-4 o
C while for silica
dndT~10
-5 o
C . As polymer is having a high dndT which is 10 times higher than silica, it can be
concluded that index modulation of polymer are more dependent on the temperature or easy to actively control. Thus it takes less power to induce thermo-optically in polymer waveguide
compared to silica waveguide [12]. In addition, polymeric materials are particularly attractive in integrated optics because of their ability to be processed rapidly, cost-effectively, and with high
yields [13-14]. Based on our previous work on photodefinable BenzoCyclobutene BCB 4024- 40 polymer in optical devices development [15-17], we have successfully demonstrates that
BCB 4024-40 polymer is a suitable material to be adopted in our future works on optical switches and attenuators.
In order to reduce the crosstalk figure, we propose a new structural design of polymer in glass optical switch structure consists of 2×2 thermo-optic MMI switch and two single couplers
MMI-VOA, with both elements integrated in series. Finite difference beam propagation method FD-BPM is employed in this work to simulate the performance of proposed design. It is shown
that the integration of MMI-VOA gives significant improvement in crosstalk performance compared with those of a conventional MMI optical switch.
2. Operation Principle and Device Structure
